There are multiple manners for a user to use a terminal device to acquire and play multimedia content. Typical manners are a manner of downloading the multimedia content to a local disk over an HTTP file download or a Peer-to-Peer (P2P) file download and then playing the multimedia content, a traditional streaming media manner (e.g., Real-time Transfer Protocol (RTP)/Real-time Transfer Protocol Control Protocol (RTCP) for data transmission and Real-time Streaming Protocol (RTSP) for play control), online live broadcast/Video on Demand over P2P streaming media manner, HTTP progressive download, and the like. Based on the HTTP progressive download, an enhanced streaming media transmission manner based on an HTTP protocol is developed, which is referred to as the HTTP streaming transmission solution. This solution supports dynamic bit rate adaptation, that is, it is capable of dynamically selecting, according to the available bandwidth between a client and a server, a media segment with a bit rate matching the available bandwidth in real time during a playing process, so as to provide a user with high-quality play experience. Therefore, this solution is also referred to as HTTP adaptive streaming (HAS) or adaptive HTTP streaming. In the 3rd Generation Partnership Project (3GPP) SA4 R9 standard, the HTTP adaptive streaming solution may further be classified into a static mode and a dynamic mode according to content-preparation modes. In the static content preparation mode, media content transmitted over HTTP serves as static content, and an HTTP server does not need to prepare content in any manner because content preparation is completed in advance; in the dynamic content service mode, the HTTP streaming server dynamically tailors streaming content for the client based on a request of the client.
During a live broadcast process, as a media segment for a following time period has not been generated yet, a media presentation description (MPD) or a playlist (for brevity, only the MPD is mentioned subsequently, but the description also applies to the playlist) cannot include acquisition information, such as a Uniform Resource Locator (URL), of the media segment for the following time period. However, if related information, such as the content encoding format, encapsulation format, resolution, bit rate, and language, of the media segment for the following time period is known, and a corresponding URL address for acquisition can be allocated in advance for a media segment for a short following time period, it is possible to provide description information of the media segment for the following time period in advance. However, content with another source may need to be inserted subsequently during the live broadcast and the accurate end time point of the live broadcast may not be known. Therefore, media presentation description information for a long following time period cannot be provided. This brings the following problem: it is probable that the media presentation description information for the following time period for live media presentation cannot be provided all at once like Video on Demand content when being accessed by the client, and the media presentation description information for the following time period needs to be gradually added in the MPD as time goes on. In this manner, the client needs to continuously acquire updated MPD to obtain the media presentation description information for the following time period and thereby has a corresponding URL to acquire a media segment and play the media segment.
The MPD may be updated in two manners. (a) Enable the MPD to include the media presentation description information for all time periods (time-line) since the live broadcast starts. This manner brings the problem that as time goes on, the MPD includes a longer time period and accordingly the MPD includes more description information. In this case, the size of the MPD increases gradually and the client needs to acquire MPD larger than the previous MPD each time requesting updated MPD. Therefore, this manner is comparatively applicable to live media presentation of a short duration. (b) Perform an update in sliding window mode: enable updated MPD to include only the description information of a media segment for a time period close to the current time point. For example, typically, only media presentation description information for the latest 10 minutes to 1 hour may be included, and media presentation description information exceeding the time period is not included in the updated MPD. In this manner, if accessing when the live broadcast starts, the client locally creates a playlist and sequentially adds time periods included in subsequent updated MPDs to the local playlist, so as to obtain a complete playlist with the time period when the live broadcast starts to the time period included in the current MPD, thereby achieving the same effect as manner (a). In manner (b), if the client accesses at a certain time point after the live broadcast starts, an updated MPD that it acquires includes only the media presentation description information for a time period close to the access time point and may not include the media presentation description information for the time period when the live broadcast starts. In this case, the client cannot seek back to an earlier time point (for example, the time shift or playback function). Therefore, when providing MPD, the HTTP streaming server needs to determine the duration of a time period of the media description information included in the MPD. The total duration of time periods included in the MPD may affect behaviors of performing play/pause and Seek operations by the client in a live broadcast session. A longer total duration of the time periods indicates a longer playlist included, a longer time period in which the client is capable of performing a pause operation without losing its location in the live broadcast playlist, and a larger time range that the client is capable of seeking. However, if MPD including a longer total duration of time periods is determined, a higher network load is brought. As the client needs to update the MPD frequently, although the size of each MPD file is generally small, the accumulation of each update is considerable.